"It's the first one built for and designed for the North American market," said Stephen Elop, Nokia's CEO. He unveiled the new phone at CES in Las Vegas.

The phone has a 4.3-inch Amoled screen and Carl Zeiss optics on the camera. The body of the phone is made of polycarbonate, a substance Nokia says it has been using for 20 years and thus has special skills using. The phone will be available in blue and black models.

Executives on stage at CES to launch the phone stressed camera quality. The back camera has a 28-millimeter focal length, meaning users can squeeze more into photos than with most camera phones. The Lumia 900 also has a front-facing camera for video conferencing.

The companies did not disclose details about when the phone would become available or how much it would cost. "We look forward to launching the Lumia 900 in the coming months," said Ralph de la Vega, president and CEO of AT&T Mobility and Consumer Markets, who appeared briefly at the event.

"As relates to pricing, our intention is to enter the U.S. market with the Lumia 900 aggressively," Elop said when asked about pricing.

Nokia worked closely with app developers to create apps that really take advantage of the Windows Phone "Metro" user interface, said Kevin Shields, a senior vice president at Nokia. He showed off ESPN and CNN apps that Nokia helped develop. "We're going to make the sports nuts who are Lumia customers delighted," Shields said.

At an event earlier in the day, Nokia positioned this launch as its effort to reenter the U.S. market. AT&T appears to have high hopes for the launch. "Nokia is going to be back in the U.S. in a very big way," de la Vega said. AT&T has sold the most Windows Phones of any operator in the U.S.

But according to Microsoft CEO Steve Ballmer, who also appeared at that event, that doesn't mean sales have been great. "AT&T has sold more Windows Phones than anybody, but we have a lot of room to go in terms of selling Windows Phones," he said.

Both Microsoft and Nokia are hoping to boost lagging performance in mobile phones. Microsoft had just 1.5 percent share of the worldwide smartphone market in the third quarter of 2011, down from 2.7 percent in the previous year, according to research from Gartner. Nokia was still the top phone maker, with 23.9 percent share of the mobile device market in the third quarter. But its share has been steadily declining over the years; it dropped from 28.2 percent in the third quarter of 2010, Gartner found.

Nokia declined to say more about additional operators that might get the Lumia 900 in the future. "Clearly our aspiration is to reach out to as many consumers as we can in the American market," Elop said.

T-Mobile will be the first operator in the U.S. to sell a Nokia Windows Phone model, when the Lumia 710 goes on sale on Wednesday. The phone is geared to first-time smartphone buyers and will cost just $50 after rebates. U.S. phone fans have been waiting for the Lumia 800, a higher-end Nokia Windows Phone that's been available in other parts of the world for a few months. So far, no U.S. operator has announced plans to sell that model.

Earlier on Monday, Ballmer made a surprise appearance at the AT&T Developer Summit and announced that HTC and Nokia would make the first LTE Windows Phones.